SOLVED: Hum in DIY micro Kevin Gilmore class-A amp. Please help

Hi DIY gurus,

Few years back I built a micro KGCA amp.  The amp sounded excellent but it had a hum which was annoying so slowly I moved away from it.  Recently I bought a well known solid state amp (don't want to name it) and I took out my KGCA to compare with it and it compared extremely well apart from the hum.  So I decided to do whatever I can to fix it as I had spent considerable time and money building it in the first place.

The power supply (PS) and the amp pcb are housed in a small plastic cabinet and since the cabinet is pretty small, the pcb goes half-way over the PS.  I know this is going to raise some eyebrows.

Here are some findings

1)  When the amp pcb is kept beside the the PS instead of on top, the hum goes away.  This is expected I guess.

2)  Here is the interesting one. 

     a)  When I touch any of the wires going to the volume potentiometer (pot) or the heat sink, it starts humming. 

     b)  In fact I don't have to touch it. If I move my hand close to the pcb or wires without touching anything, it start humming. 

     c)  If I attach a wire to the ground of the PS and hold it in one hand, and then touch anything with the other hand be it the pot or the heatsink or the wires, no hum!!  So the hum may not be just the proximity to the PS.

I was reading up on the net and the issue seemed similar to ground loop or EM interference.  I tried connecting the ground from the PS to the metal covering of the volume pot but that didn't help.  I was thinking of wrapping the ps in aluminium foil tape but then there could be a major risk of shorting something. 

I am at a loss.  Any ideas or suggestions greatly appreciated.

Regards

Priyo

Thanks to everybody for your suggestion.  Amp is totally silent and sounds awesome.  Below is what I did.  All of these helped.

1)  Grounded the volume control pot's body

2)  Rotated the torroidal transformer until it had minimum noise.  Interesting that the direction of the transformers makes such a difference.  Did not move to a different enclosure. 

3)  Now the one that made the most difference.  Wrapped a plastic plate in aluminium tin foil. Then wrapped the aluminium covered plastic plate in insulating electrical tape.  Placed this plate in between the PS pcb and the amp pcb and moved around the wires neatly.  

After the above 3, the hum went down to zero.  I also tried wrapping the input wires with aluminium foil.  This caused way more hum until I accidentally grounded the shield which brought down the hum to zero again. I didn't finally shield them as the hum was already gone.  Important lesson is that for metallic shielded wires, the shield needs to be grounded.